Conventionally, in bone-cutting operations and other like operations in neurosurgery and plastic surgery, such instruments or tools as Kerrison forceps, rongeur, drills, surgical knives, and gouges (round type only) have been used in order to cut and separate biological tissues, particularly hard bone tissue, cartilage tissue, and periosteum. However, there were disadvantages that the efficiency in tissue-cutting/separating work was low and long time was required, and heavy work load was imposed on the surgeon and a high level of technique was required.
Next, cutting tools, which use an electromotor or a pneumatic motor as a driving source, are used particularly for cutting hard bones. They make the rotational movement of the motor change to a linear movement by a cam or the like, and vibrate a cutting tool the tip of which is provided with saw teeth which are made of a metal. The amplitude of the vibraion of the cutting tool is on the order of 0.5 to 5 mm, while the frequency is on the order of 1 to 5 KHz. The cutting speed is affected by the magnitude of amplitude. However, since the cutting tool is vibrated at an amplitude on the order of 0.5 to 5 mm, if the cutting tool should be brought into contact with nervous tissue during cutting, there was a fear of injuring nervous tissue.
Further, a number of surgical instruments which employ ultrasonic waves have been developed. Surgical instruments have been known (for example, Japanese Patent Examined Publication No. 47-39197, and U.S. Pat. No. 3,589,363) in which the working portion connected to a source of ultrasonic vibration is ultrasonically vibrated, and soft tissues, other than elastic tissues such as blood vessels, with which the working portion is brought into contact, are crushed and removed by suction. A surgical instrument (for example, Japanese Patent Examined Publication No. 51-46,990, and U.S. Pat. No. 4,188,952) was developed for use in cutting and separating hard and soft tissues, and is connected to the source of ultrasonic vibration and provided with a metal working portion having saw-like cutting teeth. A surgical instrument (for example, U.S. Pat. Nos. 2,714,890, 2,845,072, and 3,832,776) is provided with a knife-shaped blade made of metal and a surgical instrument which has a bone marrow cavity rasp, for example, the SONIC SURGERY System which is a product of Howmedica Inc.
However, it is difficult to apply surgical instruments which crush and remove through suction biological tissues by utilizing ultrasonic vibration to cut biological tissues, particularly hard tissue such as bones. Further, although it is possible to apply a surgical instrument having a bone marrow rasp connected to a source of ultrasonic vibration to the cutting of soft bones and hard bones, it is difficult to apply it to the cutting and separating of periosteum, etc., since it may break biological tissue on the location of the cut surface due to the frictional heat of the rasp. In the case of a continuous operation, the surgical instrument is heated due to the ultrasonic vibrations and the mechanical strength of the surgical instrument per se is reduced. Furthermore, a surgical instrument which has a metal working portion connected to a source of ultrasonic vibration involves the fear that the cutting speed may be reduced during the process of repetitively cutting hard tissue such as bones because of deformation due to wear of the cutting teeth of the blade. In addition, since the working portion which is brought into contact with biological tissue is made of metal, there is a risk that a simple electrical fault could cause an electrical shock to the nervous tissue.
The present invention is aimed at providing, for solving such problems of the conventional surgical instruments, a surgical instrument for use in cutting and separating of biological tissue, particularly periosteum, etc., which allows the efficiency of the cutting and separating work by employing ultrasonic vibration to be improved, prevents biological tissue brought into contact with the working portion from being destroyed and broken due to frictional heat generated during the cutting and separating work, prevents mechanical strength of the working portion from being reduced due to heat generation during a continuous operation, or prevents the metal blade of the surgical instrument from being worn and deformed and prevent electrical shocks from being applied to nervous tissue in the event of a simple electric fault.